As a text output, the value from variable $to (source: #_ATT{deadline} = 18/05/2018) is passed correctly, but as soon as you want to use it as a date to compare with the current date, you can not.
Strangely not “18.05.2018” used, but “#_ATT{deadline}” as text – so no date comparison can work.

unfortunately this bug arose by us trying to fix another bug where users were trying to create shortcodes with formats within it e.g.

[events_list]#_EVENTNAME<br>[/events_list]

Previously you’d end up with a list containing the name of the same event since #_EVENTNAME was parsed before the shortcode. 5.8.1.2 ‘fixed’ this by parsing shortcodes first, but inadvertedly created this bug you’re reporting since any arguments are not parsed yet.

We’re going to revert this in the next update. However, since we’re in a bit of a limbo with timezone integration it may be a few more weeks between the next update, so the short-term solution would be to manually edit and comment out or remove this line on /events-manager/classes/em-events.php (line 1710):